A sulfonium salt compound is a substance that generates an acid on exposure to energy radiation, such as light, and is used, for example, as a photo-acid generator in photolithographic resist compositions used in the formation of electronic circuits having semiconductors or as a cationic polymerization initiator in photopolymerizable compositions, such as stereolithographic resin compositions, paint, coatings, and adhesives.
Patent Literatures 1 to 3 below each disclose an aromatic sulfonium salt compound, a photo-acid comprising the compound, and a photopolymerizable composition containing the photo-acid generator. However, the photo-acid generators disclosed are insufficient in developing properties and when, in particular, used as a negatively working resist, have difficulty in micropatterning.